Re: [dm-devel] [RFC] Message ioctl direct to device

From: Alasdair G Kergon <agk redhat com>

To: Daniel Phillips <phillips redhat com>

Cc: dm-devel redhat com

Subject: Re: [dm-devel] [RFC] Message ioctl direct to device

Date: Fri, 9 Jul 2004 22:05:58 +0100

On Fri, Jul 09, 2004 at 04:16:32PM -0400, Daniel Phillips wrote:
> Let's work though this nice and slowly please. You're saying that LVM2
> can go change the table, e.g., by inserting a mirror for pvmove, at any
> time.
Yes. Applications like LVM2 should be free to insert new layers & split
targets up whenever they want.
> But if that happens, we can end sending the message to the wrong
> target (e.g., a temporary mirror instead of the snapshot target)
This is one of the complexities still to be worked out: how we
see that the message (ie the ioctl "payload") gets passed on down
to the right layer.
If it's done by index and there are multiple layers - no chance.
If it's done by sector, I think it's possible.
And it probably requires that the "payload" strings conform to a
standard too, so that the right target knows to intercept them.
[There are alternative approaches; intend to explore each of them
before making decisions.]
Alasdair
--
agk redhat com